Final answer:
To prove that DE || CE, we use the Corresponding Angles Postulate by noting that AD || BC and ∠BCD = ∠CBE. This implies that ∠ADC = ∠CBE, which in turn confirms the parallel lines DE || CE.
Step-by-step explanation:
To prove that DE || CE, we can use the Corresponding Angles Postulate. Since AD || BC and ∠BCD = ∠CBE, we can conclude that ∠ADC = ∠CBE as corresponding angles. Therefore, by the Corresponding Angles Postulate, DE || CE.